Every year, industrial installations suffer extensive material damage, caused by fires and/or explosions. Occasionally even, this damage is accompanied by loss of life.
Efforts directed towards preventing these risks must thus be made and European Directive 1999/92/EC of 16 Dec. 1999 addresses this matter.
Mixtures of air with one or more flammable substances, defined under the term “explosive atmospheres” by European Directive 1999/92/EC of 16 Dec. 1999, may undergo explosion or ignition when they are stored at ambient or higher temperatures in confined or semi-confined environments.
Such atmospheres may be present in certain volumes such as grain silos, in the interstitial grain space, in the empty part of the storage cells above the grain, and also in the silo handling galleries in the empty “diamond” cells or intercalations or other confined spaces.
These explosive atmospheres may consist of hydrocarbons and air, of pyrolysis products and air or of aerobic or anaerobic fermentation of wet grain or of dusts arising from grain cleaning, drying or handling operations.
Other open-cast silos are also concerned since the atmosphere inside the stored mixture is explosive and can give rise to “smouldering fires” inside the stored mass or to a fire at the surface of the stored pile.
Explosive atmospheres may also be present in stocks of fertilizers, of animal or plant meals/powders, vehicle tanks, driftways, etc.
Thus, it is important to detect the risk of explosion of these explosive atmospheres.
Document WO 89/08253 describes a process and apparatus for determining whether or not a fuel can cause an explosion under the conditions present in a diesel engine. This phenomenon is studied by subjecting the fuel to exposure in the presence of a mixture of oxidizing gases while gradually increasing the temperature. In a second step, a catalytic post-oxidation reaction to CO2 and water is carried out and a detector continuously measures the amount of CO2 produced. The cetane number of the fuel is determined by analysing databases on a statistical model.
Similar devices are described in document WO98/18001, in which different detecting elements (sensors) are used, making it possible to determine the critical proportion of the various components in measuring chambers up to the point of forming an explosive mixture.
However, these various systems are based on a comparison relative to a reference generally determined for a specific volume and mix of fuels.
The document JP-A-09304310 describes a process for preventing the risk of spontaneous ignition in which the temperature is measured in the sample holding container and in which the critical moment is determined both on the basis of the time which has elapsed and by comparing the measured temperature with the critical temperature. The critical moment of the sample in said process is therefore not literally known.